Erythroblastic island in bone marrow

Scheme electron microscopy. Different stages of maturing erythroblasts (2) are exposed in this scheme. The centrally localized phagocytic reticular cell (1) has many long cytoplasmic extensions that form a network with similar cells within the bone marrow. Its nucleus is irregular. The cytoplasm has a moderate amount of organelles however with a distinct variety of lysosomal structures (4). At (5) a large phagolysosome is shown that contains an expelled nucleus of an erythroblast. Different stages of maturing erythroblasts are spread around and close to the reticular cell. (3) indicates a pro-erythroblast (15-20 m) with 2-3 nucleoli, large mitochondria and numerous polysomes. (6) a basophilic erythroblast (12-18 m) or early normoblast with clumped heterochromatin in the nucleus (mitosis) and numerous polysomes. The polychromatic erythroblast or intermediate normoblast (2A) (10-12 m) marks the onset of hemoglobin synthesis in the maturing stage concomitant with a general decrease in amount of all organelles. At this time nuclear clumping starts to take place. At (2B) the orthochromatic erythroblast or late normoblast (8-12 m) shows the early stage of extrusion of the pyknotic nucleus. At (2C) an anucleate reticulocyte is shown close to an expelled pyknotic nucleus (2D).